mesh.tet.generate: mesh every body of the open design by default

The Tet Mesh form opened with {} and failed with "give either body (with
tolerance) or surface", so a first-time user could not mesh a part
without knowing its body name and a chordal tolerance. The tet mesher
now takes its bodies as the hex meshers do: every body of the open
design by default, one named body, or an imported surface, with the
tessellation tolerance defaulting to 1e-3 of each body's diagonal. With
several bodies an error names the body it is about. The reply keeps its
totals (kind, counts, first labels, volumes) and lists each body's
counts, size and quality report under `bodies`.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

crates/engine/src/cmd/hex.rs

@@ -33,7 +33,7 @@ pub(super) struct Input<'a> {
     pub(super) name: String,
     pub(super) mesh: Cow<'a, SurfaceMesh>,
     surfaces: Vec<Option<Surface>>,
-    face_names: Vec<String>,
+    pub(super) face_names: Vec<String>,
     pub(super) diagonal: f64,
 }